Dynamic Modeling and Simulation of Microturbine Generating System for Stability Analysis in Microgrid Networks

Abbas Khorshidi1*, Mahdi Zolfaghari1, Maryam Akhavan Hejazi2

1Department of Electrical Engineering, University of Allameh Feiz Kashani, Kashan, Iran 2Department of Electrical Engineering, University of Kashan, Kashan, Iran

*Corresponding Author Email: Abbaskhorshidi62@yahoo.com

Abstract

This paper presents the dynamic modeling and simulation of a microturbine generation (MTG) system, the nonrenewable source of energy suitable for isolated as well as grid-connected operation in microgrid networks. A microgrid is defined as an independent low or medium- voltage distribution network comprising various DGs, energy storages, and controllable loads. The MTG system consisting of a permanent magnet synchronous generator (PMSG) coupled with a microturbine (MT) which is suitable for stability studies in microgrid networks is modeled and simulated using MATLAB/SIMULINK.

Keywords: Microturbine, Microgrid, Stability. Introduction

Distributed energy resources (DERs), such as fuel cells, microturbines, and photovoltaic systems offer many advantages for power systems (Jiayi et al., 2008; Lasseter, 2002). For example, they can effectively mitigate peak demand, increase reliability against power system faults, and improve power quality (PQ) via sophisticated control schemes. Accordingly, distributed generators (DGs) have been installed in power systems and tested for better configurations and control schemes. The concept of a microgrid has been proposed in order to solve the common interconnection problems of individual DGs in various power systems (Lasseter, 2002; Piagi & Lasseter, 2004). A microgrid is defined as an independent low or medium-voltage distribution network comprising various DGs, energy storages, and controllable loads that can be operated in three distinct modes: 1) grid-connected, 2) islanded (autonomous), and 3) transition mode (Tsikalakis & Hatziargyriou, 2008; Soultanis et al., 2008).

A microgrid can be thought of as a controllable subsystem to the utility, and can satisfy customer requirements, such as local reliability enhancement, feeder-loss reduction, local voltage regulation, and increased efficiency through the use of waste heat (Hannet & Afzal Khan, 1993a). Some of the operational aspects which require full understanding are voltage control, stability, system protection etc. Such studies require accurate modeling of distributed generation (DG) sources including distribution system (Scott, 1998). Distributed generation using microturbine is a typical and practical solution because of its environment-friendliness and high energy efficiency (Rowen, 1983). Various applications such as peak saving, co-generation, remote power and premium power will make its use worldwide. Generally MTG systems range from 30 to 400 kilowatts (Al-Hinai & Feliachi, 2002; Borbely & Kreider, 2001), while conventional gas turbines range from 500 kW to more than 300 MW (Hannet & Afzal Khan, 1993b; Hajagos & Berube, 2001).

Microturbines are capable of burring a number of fuels at high and low pressure levels. They generally have marginally lower electrical efficiencies than similarly sized reciprocating engine generators. Without a recuperator the overall efficiency of a microturbine is 15 to 17%, whereas with an 85% effective recuperator the efficiency can be as high as 33 to 37%. However, because of their design simplicity and relatively fewer moving parts, microturbines have the potential for simpler installation, higher reliability, reduced noise and vibration, lower maintenance requirements, lower emissions, continuous combustion and possibly lower capital costs compared to reciprocating engines (Goldstein et al., 2003; Malmquist, 1999; Jurado & Cano, 2004). An accurate model of the microturbine is therefore required to analyze the mentioned impacts. Until now, only few works were undertaken on the modeling, simulation and control of micro turbines. There is also a lack of adequate information on their performances. A dynamic model for combustion gas turbine has been discussed in (Lasseter, 2001). The dynamic behavior of the grid connected split shaft microturbine is discussed in (Al-Hinai et al., 2003). Zhu and Tomsovic (2002) the load following performance and modeling of split shaft micro turbine is discussed. A distribution system with some simple but practical control strategies is developed for the analysis of load- following service provided by microturbine (Zhu & Tomsovic, 2002). This paper presents single shaft microturbine generation system model developed in Sim power systems library of the MATLAB software.

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